Within the scope of strict legal requirements relating to the emissions of pollutants by motor vehicles, an important measure is to keep a low level of emissions of pollutants which occur during the combustion of the air/fuel mixture in the respective cylinder of the internal combustion engine. A further measure is also to use exhaust gas post-treatment systems in internal combustion engines, said systems converting into harmless substances the emissions of pollutants which are generated in the respective cylinder during the combustion process of the air/fuel mixture. For this purpose, exhaust gas catalytic converters are used which convert carbon monoxide, hydrocarbons and nitrogen oxides into harmless substances.
Both the aimed-for influencing of the generating of the emissions of pollutants during the combustion and the conversion of the components of the pollutants with a high degree of efficiency by the exhaust gas catalytic converter require a very precisely set air/fuel ratio in the respective cylinder. In particular in view of the fact that the exhaust gas catalytic converters are increasingly arranged very close to the engine and also in order to comply with corresponding specific legal requirements in individual countries, precise cylinder-specific setting of the air/fuel ratio is increasingly important, since the individual exhaust gas packets only mix relatively poorly because of the short mixing distance.
Increasingly stringent legal requirements with regard to the emission of limited pollutants make it necessary to allow a small tolerance in the air/fuel ratio between the individual cylinders. A large uneven distribution and an absence of compensation cause the emissions to become significantly worse or even give rise to perceptible problems with respect to driving capabilities.
Furthermore, there are legal requirements for the cylinder-selective unequal distribution in the air/fuel ratio to be detected incrementally in an increasing portion of the respective vehicles in relation to the vehicle fleets of the respective manufacturers, said uneven distribution causing predefined emission limiting values to be exceeded.
DE 10 2004 004 291 B3 discloses using cylinder-specific lambda control, by means of which the individual deviations of the respective cylinder-specific air/fuel ratios from an average air/fuel ratio are to be minimized. A measurement signal of an exhaust gas probe which is arranged in an exhaust gas section, and which is characteristic of the air/fuel ratio in the respective cylinder, is detected at a predefined crankshaft angle with respect to a reference position of the piston of the respective cylinder and is assigned to the respective cylinder. By means of the cylinder-specific lambda controller, a manipulated variable for influencing the air/fuel ratio in the respective cylinder as a function of the measurement signal generated for the respective cylinder is generated. The predefined crankshaft angle is adapted as a function of an instability criterion of the controller.
DE 10 2006 0263 90 A1 discloses an electronic control device for the control of the internal combustion engine in a motor vehicle having an unsmooth running determining unit and having an injection quantity correction unit, wherein a defined group of cylinders is assigned one lambda probe. The injection quantity correction unit is configured such that the injection quantity of one cylinder, which is to be tested, of the defined group can be adjusted in the lean direction by a difference adjustment value which is assigned to an unsmooth running difference value, and the injection quantity of at least one of the other cylinders which is assigned to the same lambda probe is correspondingly adjusted in the rich direction, with the result that overall a predefined lambda value of this group, preferably a lambda value of at least approximately 1, is attained. The injection quantity correction value is also configured in such a way that in this way a cylinder-specific difference adjustment value can be set for each cylinder of the defined group, and that cylinder-specific correction values can be determined by setting the cylinder-specific difference adjustment values in a ratio with respect to one another.